Photostable cosmetic screening composition containing a UV-A screening agent and an alkyl β, β-diphenylacrylate or α-cyano-β,β-diphenylacrylate

ABSTRACT

A photostable cosmetic screening composition and process for protection of the human epidermis against UV rays of wavelengths between 280 and 380 nm, the composition having, in a cosmetically acceptable vehicle containing at least one fatty phase, 1 to 5% by weight of a dibenzoylmethane derivative and at least 1% by weight of an alkyl β-β-diphenylacrylate or α-cyano-β-β-diphenylacrylate of formula (I), the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative being not less than 0.8.

This is a continuation of application Ser. No. 07/937,886, filed as PCT/FR91/00112 Feb. 13, 1991, published as WO91/11989 Aug. 22, 1991, now abandoned.

The present invention relates to a photostable cosmetic composition intended for protecting the skin against UV radiation, containing in combination a UV-A screening agent and an alkyl β,β-diphenylacrylate or α-cyano-β,β-diphenylacrylate, to its use for the protection of the skin against UV rays and to a process for stabilizing the UV-A screening agent with an alkyl β,β-diphenylacrylate or α-cyano-β,β-diphenylacrylate.

It is known that light radiation of wavelengths between 280 nm and 400 nm permits tanning of the human epidermis, and that rays of wavelengths between 280 and 320 nm, known by the name of UV-B, cause erythema and burning of the skin which can impair the development of the tan; this UV-B radiation must hence be screened out.

It is also known that UV-A rays, of wavelengths between 320 and 400 nm, causing tanning of the skin, are liable to induce adverse changes in the latter, in particular in the case of sensitive skin or skin continually exposed to solar radiation. UV-A rays cause, in particular, a loss of elasticity of the skin and the appearance of wrinkles, leading to premature ageing. They promote a triggering of the erythematous reaction or enhance this reaction in some subjects, and can even be the source of phototoxic or photoallergic reactions. It is hence also desirable to screen out UV-A radiation.

French Patents No. 2,326,405 and No. 2,440,933 and European Patent No. 114,607 describe dibenzoylmethane derivative as UV-A screening agents. It is proposed in these patents to combine these UV-A screening agents with various UV-B screening agents with the object of absorbing all the UV radiation of wavelengths between 280 and 380 nm.

Unfortunately, when they are used in combination with these UV-B screening agents, the dibenzoylmethane derivatives describe in the abovementioned patents do not always possess sufficient photochemical stability to ensure constant protection during a prolonged exposure to the sun, which necessitates repeated applications at regular and frequent intervals if it is desired to obtain an effective protection of the skin against UV rays.

The Applicant has discovered that, by combining the abovementioned dibenzoylmethane derivatives with an alkyl β, β-diphenylacrylate or α-cyano-β,β-diphenylacrylate of formula ##STR1## in well-defined proportions and in a well-defined mole ratio, an exceptional photochemical stability of the dibenzoylmethane derivatives was surprisingly obtained. In addition, such a combination imparts to the screening composition containing it a large sun protection factor as well as good persistence; persistence may be defined as a small change in the protection factor after the subject who has received an application of the screening composition has bathed.

In the general formula (I), the substituents R₁ to R₃ can assume the following meanings:

R₁ and R'₁, which may be identical or different, represent a hydrogen atom, a straight- or branched-chain C₁ -C₈ alkoxy radical or a straight- or branched-chain C₁ -C₄ alkyl radical,

R₁ and R'₁ being in the para or meta position;

R₂ represents a straight- or branched-chain C₁ -C₁₂ alkyl radical; and

R₃ represents a hydrogen atom or a CN radical.

Among straight- or branched-chain C₁ -C₈ alkoxy radicals, there may be mentioned, for example, methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, tert-butoxy, n-amyloxy, isoamyloxy, neopentyloxy, n-hexyloxy, n-heptyloxy, n-octyloxy and 2-ethylhexyloxy radicals.

Among straight- or branched-chain C₁ -C₄ -alkyl radicals, there may be mentioned, more especially, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl radicals. For C₁ -C₁₂ alkyl radicals, there may be mentioned, by way of example, in addition to those mentioned above, n-amyl, isoamyl, neopentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, decyl and lauryl radicals.

Among the compounds of general formula (I), the following compounds are more especially preferred:

1--2-ethylhexyl α-cyano-β,β-diphenylacrylate,

2--ethyl α-cyano-β,β-diphenylacrylate,

3--2-ethylhexyl-β,β-diphenylacrylate,

4--ethyl β,β-bis(4-methoxyphenyl)acrylate.

Among the dibenzoylmethane derivatives mentioned in the above patents, there may be mentioned especially:

2-methyldibenzoylmethane

4-methyldibenzoylmethane

4-isopropyldibenzoylmethane

4-tert-butyldibenzoylmethane

2,4-dimethyldibenzoylmethane

2,5-dimethyldibenzoylmethane

4,4'-diisopropyldibenzoylmethane

4-tert-butyl-4'-methoxydibenzoylmethane

2-methyl-5-isopropyl-4'-methoxydibenzoylmethane

2-methyl-5-tert-butyl-4'-methoxydibenzoylmethane

2,4-dimethyl-4'-methoxydibenzoylmethane

2,6-dimethyl-4-tert-butyl-4'-methoxydibenzoylmethane.

Among the dibenzoylmethane derivatives mentioned above, special preference is given to 4-tert-butyl-4'-methoxydibenzoylmethane, sold by the company GIVAUDAN under the name "PARSOL 1789", and 4-isopropyldibenzoylmethane, sold by the company MERCK under the name "EUSOLEX 8020".

The derivatives of formula (I) in which R₃ =CN, R₁, R'₁ and R₂ having the meanings stated above, may be prepared according to the process described in U.S. Pat. No. 3,215,724.

The derivatives of formula (I) in which R₃ =H, R₁, R'₁ and R₂ having the meanings stated above, may be prepared according to the process described by L. H. KLEMM et al. in J. Org. Chem., 23 (1958) page 344. This process enables the ethyl esters (R₂ =C₂ H₅) to be prepared. To prepare the other esters (R₂ ≠C₂ H₅), the transesterification of the ethyl ester with an alcohol R₂ OH (R₂ having the meaning stated above except for ethyl) is performed in the presence of para-toluenesulphonic acid.

By virtue of their lipophilic character, the screening agents used distribute uniformly in conventional cosmetic vehicles containing at least one fatty phase, and can thus be applied on the skin to form an effective protective film.

The subject of the present invention is hence a photostable cosmetic composition protecting the skin against UV radiation of wavelengths between 280 and 380 nm, comprising, in a cosmetically acceptable vehicle containing at least one fatty phase, 1 to 5% by weight of dibenzoylmethane derivative and at least 1% by weight of compound of formula (I), the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative being not less than 0.8, and preferably not less than 1.2.

For reasons of solubilization of the compounds in the composition, this ratio is preferably not more than 8, but this upper limit is not critical.

The subject of the present invention is also a process for protecting the human epidermis against UV rays of wavelengths between 280 and 380 nm, consisting in applying to the skin an effective quantity of a cosmetic composition as defined above.

Another subject of the present invention consists of a process for stabilizing dibenzoylmethane derivatives with respect to UV radiation by means of a compound of formula (I), in which process at least 1% by weight of compound of formula (I) is used to stabilize 1 to 5% by weight of dibenzoylmethane derivative, the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative being not less than 0.8.

On account of the lipophilic character of the compounds of formula (I) and dibenzoylmethane derivatives, the cosmetic compositions according to the invention contain at least one fatty phase. They can take the form of oily or oleoalcoholic lotions or the form of fatty or oleoalcoholic gels, of solid sticks, of emulsions such as a cream or milk or of vesicular dispersions of ionic or nonionic amphiphilic lipids; they can be packaged as an aerosol.

As a solubilization solvent, an oil or wax, lower polyol or monohydric alcohol or mixtures thereof may be used. Especially preferred monohydric alcohols or polyols are ethanol, isopropanol, propylene glycol and glycerol.

The cosmetic composition according to the invention, intended for protecting the human epidermis against ultraviolet rays, can contain the cosmetic adjuvants usual in this type of composition, such as thickeners, emollients, humetants, surfactants, preservatives, antifoams, oils, waxes, lanolin, fragrances, propellants, colorings and/or pigments whose function is to color the composition itself or the skin, or any other ingredient customarily used in cosmetics.

In addition to the compound of formula (I) and the dibenzoylmethane derivative, the composition can contain other lipophilic UV screening agents.

An embodiment of the invention is an emulsion in the form of a cream or milk comprising, in addition to the compound of formula (I) combined with the dibenzoylmethane derivative, fatty alcohols, fatty acid esters, and in particular fatty acid triglycerides, fatty acids, lanolin, natural or synthetic oils or waxes and emulsifiers, in the presence of water.

Another embodiment consists of oily lotions based on fatty acid esters, oils and/or natural or synthetic waxes, or of oleoalcoholic lotions based on oils, waxes or fatty acid esters such as fatty acid triglycerides and on lower alcohols such as ethanol or glycols such as propylene glycol and/or polyols such as glycerol.

The oleoalcoholic gels comprise an oil or wax, a lower polyol or alcohol such as ethanol, propylene glycol or glycerol and a thickener such as silica.

The solid sticks consist of fats such as natural or synthetic waxes and oils, fatty alcohols, fatty acid esters and lanolin.

In the case of a composition packaged as an aerosol, conventional propellants such as alkanes, fluoroalkanes and chlorofluoroalkanes are used.

When the composition takes the form of an emulsion or vesicular dispersion, the aqueous phase can contain water-soluble UV screening agents such as benzene-1,4-bis(3-methylidene-10-camphorsulphonic acid) [sic], 2-phenylbenzimidazole-5-sulphonic acid or 2-hydroxy-4-methoxybenzophenone-5-sulphonic acid (UVINUL MS 40), these acids being salified or otherwise.

The examples which follow are intended as illustrations of the invention, no limitation of the latter being, however, implied.

EXAMPLE 1

Nonionic emulsion

    ______________________________________                                         2-Ethylhexyl α-cyano-β,β-diphenylacrylate                                                7.5    g                                             (UVINUL N 539)                                                                 4-tert-Butyl-4'-methoxydibenzoylmethane                                                                  1.5    g                                             (PARSOL 1789)                                                                  Mixture of cetyl/stearyl alcohol and                                                                     7.0    g                                             cetyl/stearyl alcohol oxyethylenated with                                      33 moles of ethylene oxide                                                     Mixture of glyceryl mono-, di- and                                                                       2.0    g                                             tristearates                                                                   Triglycerides of C.sub.8 -C.sub.12 fatty acids                                                           30.0   g                                             (Miglyol 812)                                                                  Polydimethylsiloxane      1.5    g                                             Cetyl alcohol             1.5    g                                             Distilled water q.s.      100    g                                             ______________________________________                                    

This emulsion is prepared according to conventional techniques, by dissolving the screening agents in the fatty phase containing the emulsifiers, heating this fatty phase to about 80°-85° C. and adding with brisk stirring the water heated beforehand to about 80° C.

EXAMPLE 2

Sun oil

The following ingredients are mixed, heating, where appropriate, to 40°-45° C. in order to homogenize:

    ______________________________________                                         2-Ethylhexyl β,β-diphenylacrylate                                                              6.0    g                                             4-tert-Butyl-4'-methoxydibenzoylmethane                                                                  3.0    g                                             (PARSOL 1789)                                                                  Isopropyl myristate q.s.  91.0   g                                             ______________________________________                                    

EXAMPLE 3

Sun oil

The following sun oil is prepared in the same manner as in Example 2:

    ______________________________________                                         Ethyl β,β-bis(4-methoxyphenyl)acrylate                                                         6.0    g                                             4-tert-Butyl-4'-methoxydibenzoylmethane                                                                  3.0    g                                             (PARSOL 1789)                                                                  Isopropyl myristate q.s.  91.0   g                                             ______________________________________                                    

EXAMPLE 4

Nonionic emulsion

    ______________________________________                                         2-Ethylhexyl β,β-diphenylacrylate                                                               6.0    g                                            4-tert-Butyl-4'-methoxydibenzoylmethane                                                                   1.5    g                                            Mixture of cetyl/stearyl alcohol and cetyl/                                                               7.0    g                                            stearyl alcohol oxyethylenated with 33 moles                                   of ethylene oxide                                                              Mixture of glyceryl mono-, di- and                                                                        2.0    g                                            tristeareates                                                                  Triglycerides of C.sub.8 -C.sub.12 fatty acids                                                            30.0   g                                            (Miglyol 812)                                                                  Polydimethylsiloxane       1.5    g                                            Cetyl alcohol              1.5    g                                            Distilled water q.s.       100    g                                            ______________________________________                                    

This emulsion is prepared as in Example 1.

EXAMPLE 5

Water-in-oil nonionic emulsion

    ______________________________________                                         Ethyl β,β-bis(4-methoxyphenyl)acrylate                                                          3.0    g                                            4-tert-Butyl-4'-methoxydibenzoylmethane                                                                   2.0    g                                            Mixture of cetyl/stearyl alcohol and cetyl/                                                               7.0    g                                            stearyl alcohol oxyethylenated with 33 moles                                   of ethylene oxide                                                              Mixture of glyceryl mono-, di- and                                                                        2.0    g                                            tristearates                                                                   Triglycerides of C.sub.8 -C.sub.12 fatty acids                                                            30.0   g                                            (Mygliol [sic] 812)                                                            Polydimethylsiloxane       1.5    g                                            Cetyl alcohol              1.5    g                                            Distilled water q.s.       100    g                                            ______________________________________                                    

This emulsion is prepared as in Example 1.

EXAMPLE 6

Oil-in-water emulsion

    ______________________________________                                         2-Ethylhexyl α-cyano-β,β-diphenylacrylate                                                 5.0    g                                            (UVINUL N 539)                                                                 4-Isopropyldibenzoylmethane (EUSOLEX 8020)                                                                3.0    g                                            Mixture of cetyl/stearyl alcohol and cetyl/                                                               7.0    g                                            stearyl alcohol oxyethylenated with 33 moles                                   of ethylene oxide, sold by the company HENKEL                                  under the name "SINNOWAX AO"                                                   Non-self-emulsifying mixture of glyceryl                                                                  2.0    g                                            mono- and distearates                                                          Cetyl alcohol              1.5    g                                            Silicone oil               1.5    g                                            Liquid paraffin            16.0   g                                            Glycerol                   20.0   g                                            Fragrance, preservative q.s.                                                   Water q.s.                 100    g                                            ______________________________________                                    

The emulsion is produced by adding the fatty phase containing the screening agents and the emulsifiers at approximately 80° C. to the aqueous phase brought to the same temperature and with rapid stirring.

EXAMPLE 7

Oil-in-water emulsion

    ______________________________________                                         2-Ethylhexyl α-cyano-β,β-diphenylacrylate                                                 2.0    g                                            (UVINUL N 35)                                                                  4-tert-Butyl-4'-methoxydibenzoylmethane                                                                   1.0    g                                            (PARSOL 1789)                                                                  Mixture of cetyl/stearyl alcohol and cetyl/                                                               7.0    g                                            stearyl alcohol oxyethylenated with 33 moles                                   of ethylene oxide, sold by the company HENKEL                                  under the name "SINNOWAX AO"                                                   Non-self-emulsifying mixture of glyceryl                                                                  2.0    g                                            mono- and distearates                                                          Cetyl alcohol              1.5    g                                            Silicone oil               1.5    g                                            Liquid paraffin            20.0   g                                            Glycerol                   20.0   g                                            Fragrance, preservative q.s.                                                   Water q.s.                 100    g                                            ______________________________________                                    

This emulsion is prepared as in Example 6.

EXAMPLE 8

Oil-in-water emulsion

    ______________________________________                                         2-Ethylhexyl α-cyano-β,β-diphenylacrylate                                                8.0    g                                             (UVINUL N 539)                                                                 4-tert-Butyl-4'-methoxydibenzoylmethane                                                                  1.0    g                                             (PARSOL 1789)                                                                  Mixture of cetyl/stearyl alcohol and cetyl/                                                              7.0    g                                             stearyl alcohol oxyethylenated with 33 moles                                   of ethylene oxide, sold by the company HENKEL                                  under the name "SINNOWAX AO"                                                   Non-self-emulsifying mixture of glyceryl                                                                 2.0    g                                             mono- and distearates                                                          Cetyl alcohol             1.5    g                                             Silicone oil              1.5    g                                             Liquid paraffin           15.0   g                                             Benzene-1,4-bis(3-methylidene-10-camphor-                                                                1.0    g AS                                          sulphonic acid) [sic]                                                          Glycerol                  20.0   g                                             Fragrance, preservative q.s.                                                   Water q.s.                100    g                                             ______________________________________                                    

This emulsion is prepared as in Example 6, the water-soluble screening agent being dissolved in the aqueous phase. 

We claim:
 1. A photostable cosmetic screening composition for protection of the human epidermis against ultraviolet rays of wavelengths between 280 and 380 nm, which comprises, in a cosmetically acceptable vehicle containing at least one fatty phase, 1 to 5% by weight of a dibenzoylmethane derivative and at least 1% by weight of an alkyl β, β-diphenylacrylate or a α-cyano-β,β-diphenylacrylate of formula: ##STR2## in which R₁ and R'₁, which may be identical or different, represent a hydrogen atom, a straight- or branched-chain C₁ -C₈ alkoxy radical or a straight- or branched-chain C₁ -C₄ alkyl radical, R₁ and R'₁ being in the para or meta position; R₂ represents a straight- or branched-chain C₁ -C₁₂ alkyl radical; andR₃ represents hydrogen atom or a --CN radical, the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative being not less than 0.8.
 2. Cosmetic screening composition according to claim 1, wherein the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative is not more than
 8. 3. Cosmetic screening composition according to claim 1, wherein the dibenzoylmethane derivative is selected from the group consisting of 2-methyldibenzoylmethane, 4-methyldibenzoylmethane, 4-isopropyldibenzoylmethane, 4-tert-butyldibenzoylmethane, 2,4-dimethyldibenzoylmethane, 2,5-dimethyldibenzoylmethane, 4,4'-diisopropyldibenzoylmethane, 4-tert-butyl-4'-methoxydibenzoyl-methane, 2-methyl-5-isopropyl-4'-methoxydibenzoylmethane, 2-methyl-5-tert-butyl-4'-methoxydibenzoylmethane,2,4-dimethyl-4'-methoxy-dibenzoylmethane, and 2,6-dimethyl-4-tert-butyl-4'-methoxydi-benzoylmethane.
 4. Cosmetic screening composition according to claim 1, wherein the dibenzoylmethane derivative is selected from the group consisting of 4-tert-butyl-4'methoxydibenzoylmethane and 4-isopropyldibenzoylmethane.
 5. Cosmetic screening composition according to claim 1, wherein the alkyl β,β-diphenylacrylate or α-cyano-β,β-diphenylacrylate is selected form the group consisting of ethyl αcyano-β,β-diphenylacrylate, 2-ethylhexyl β,β-diphenylacrylate and ethyl β,β-bis(4-methoxyphenyl)acrylate.
 6. Cosmetic screening composition according to claim 1, wherein the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative is between 1.2 and
 8. 7. Cosmetic screening composition according to claim 1, which is in the form selected from the group consisting of oily and oleoalcoholic lotions, fatty and oleoalcoholic gels, solid sticks, emulsions, a vesicular dispersion of ionic or nonionic amphiphilic lipids, and aerosols.
 8. Cosmetic screening composition according to claim 1, which contains, in addition, at least one cosmetic adjuvant selected from the group consisting of thickeners, emollients, humectants, surfactants, preservatives, antifoaming agents, fragrances, oils, waxes, lower monoalcohols, lower polyols, propellants, colorants and pigments.
 9. Cosmetic screening composition according to claim 1, which constitutes an emulsion in the form of a cream or milk comprising, as a cosmetic vehicle, fatty alcohols, fatty acid, esters, and in particular fatty acid triglycerides, fatty acids, lanolin, natural or synthetic oils and waxes and emulsifiers, in the presence of water.
 10. Cosmetic screening composition according to claim 1, in the form of an emulsion or a vesicular dispersion, which contains, in addition, water-soluble UV screening agents.
 11. Cosmetic screening composition according to claim 1, which constitutes an oily lotion comprising, as a cosmetic vehicle, fatty acid esters, oils and natural or synthetic waxes.
 12. Cosmetic screening composition according to claim 1, which constitutes an oleoalcoholic lotion comprising, as a cosmetic vehicle, oils, waxes or fatty acid esters, and in particular fatty acid triglycerides, and lower polyols, alcohols and/or glycols.
 13. Cosmetic screening composition according to claim 1, which constitutes an oleoalcoholic gel comprising, as a cosmetic vehicle, a natural or synthetic oil or wax, a lower polyol or alcohol and a thickener.
 14. Cosmetic screening composition according to claim 1, wherein the composition consists essentially of the cosmetically acceptable vehicle, the dibenzoylmethane derivative and the alkyl β,β-diphenylacrylate or α-cyano-β,β-diphenylacrylate.
 15. Process for protecting the human epidermis against UV radiation of wavelengths between 280 and 380 nm, which consists in applying to the skin an effective quantity of a cosmetic screening composition as defined in claim
 1. 16. A photostable cosmetic screening composition for protection of the human epidermis against ultraviolet rays of wavelengths between 280 and 380 nm, which comprises, in a cosmetically acceptable vehicle containing at least one fatty phase, 1 to 5% by weight of a dibenzoylmethane derivative selected from the group consisting of 2-methyldibenzoylmethane, 4-methyldibenzoylmethane, 4-isopropyl-dibenzoylmethane, 4-tert-butyldibenzoylmethane, 2,4-dimethyldibenzoylmethane, 2,5-dimethyldibenzoylmethane, 4,4'-diisopropyldibenzoylmethane, 2-methyl-5-isopropyl-4'-methoxydibenzoylmethane, 2-methyl-5-tert-butyl-4'-methoxydibenzoylmethane, 2,4-dimethyl-4'-methoxydibenzoylmethane and 2,6-dimethyl-4-tert-butyl-4'-methoxydibenzoylmethane and at least 1% by weight of an alkyl β,β-diphenylacrylate or a α-cyano-β,β-diphenylacrylate of formula: ##STR3## in which R₁ and R'₁, which may be identical or different, represent a hydrogen atom, a straight- or branched-chain C₁ -C₈ alkyl radical or a straight- or branched-chain C₁ -C₄ alkyl radical, R₁ and R'₁ being in the para or meta position; R₂ represents a straight- or branched-chain C₁ -C₁₂ alkyl radical; andR₃ represents a hydrogen atom or a --CN radical, the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative being not less than 0.8.
 17. A photostable cosmetic screening composition for protection of the human epidermis against ultraviolet rays of wavelengths between 280 and 380 nm, which comprises, in a cosmetically acceptable vehicle containing at least one fatty phase, 1 to 5% by weight of a dibenzoylmethane derivative selected from the group consisting of 2-methyldibenzoylmethane, 4-methyldibenzoylmethane, 4-isopropyl-dibenzoylmethane, 4-tert-butyldibenzoylmethane, 2,4-dimethyldi-benzoylmethane, 2,5-dimethyldibenzoylmethane, 4,4'-diisopropyldi-benzoylmethane, 4-tert-butyl-4'-methoxydibenzoylmethane, 2-methyl-5isopropyl-4'-methoxydibenzoylmethane-2-methyl-5-tert-butyl-4'-methoxydibenzoylmethane, 2,4-diemthyl-4'-methoxydibenzoylmethane and 2,6-dimethyl-4-tert-butyl-4'-methoxydibenzoylmethane and at least 1% by weight of an alkyl β,β-diphenylacrylate or a α-cyano-β,β-diphenylacrylate of formula: ##STR4## in which R₁ and R'₁, which may be identical or different, represent a hydrogen atom, a straight- or branched-chain C₁ -C₈ alkoxy radical or a straight- or branched-chain C₁ -C₄ alkyl radical, R₁ and R'₁ being in the para or meta position; R₂ represents a straight- or branched-chain C₁ -C₁₂ alkyl radical; andR₃ represents a hydrogen atom or a --CN radical, with the proviso that R₃ represents a hydrogen atom when R₁ and R'₁ represents a hydrogen atom and R₂ represents a 2-ethylhexyl radical, the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative being not less than 0.8.
 18. A photostable cosmetic screening composition for protection of the human epidermis against ultraviolet rays of wavelengths between 280 and 380 nm, which comprises, in a cosmetically acceptable vehicle containing at least one fatty phase, 1 to 5% by weight of a dibenzoylmethane derivative, said dibenzoylmethane derivative being selected from the group consisting of 2-methyldibenzoylmethane, 4-methyldibenzoylmethane, 4-isopropyldibenzoylmethane, 4-tert-butyldibenzoylmethane, 2,4-dimethyldibenzoylmethane, 2,5-dimethyldibenzoylmethane, 4,4'-diisopropyldibenzoylmethane, 2-methyl-5-isopropyl-4'-methoxydibenzoylmethane, 2-methyl-5-tert-butyl-4'-methoxydibenzoylmethane, 2,4-diemthyl-4'-methoxydibenzoylmethane and 2,6-dimethyl-4-tert-butyl-4'-methoxydibenzoylmethane and at least 1% by weight of an acrylate selected from the group consisting of 2-ethylhexyl-α-cyano-β,β-diphenylacrylate, ethyl α-cyano-β,β-diphenylacrylate, 2-ethylhexyl β,β-diphenylacrylate and ethyl β,β-bis(4-methoxyphenyl)acrylate, the mole ratio of the acrylate to the dibenzoylmethane derivative being not less than 0.8.
 19. A photostable cosmetic screening composition for protection of the human epidermis against ultraviolet rays of wavelengths between 280 and 380 nm, which consists essentially of a cosmetically acceptable vehicle containing at least one fatty phase, 1 to 5% by weight of a dibenzoylmethane derivative, said dibenzoylmethane derivative being selected from the group consisting of 2-methyldibenzoylmethane, 4-methyldibenzoylmethane, 4-isopropyldibenzoylmethane, 4-tert-butyldibenzoylmethane, 2,4-dimethyldibenzoylmethane, 2,5-diemthyldibenzoylmethane, 4,4'-diisopropyldibenzoylmethane, 4-tert-butyl-4'-methoxydibenzoylmethane, 2-methyl-5-isopropyl-4'-methoxydibenzoylmethane, 2-methyl-5-tert-butyl-4'-methoxydibenzoylmethane, 2,4-dimethyl-4'-methoxydibenzoylmethane and 2,6-diemthyl-4-tert-butyl-4'-methoxydibenzoylmethane and at least 1% by weight of an acrylate selected from the group consisting of ethyl α-cyano-β,β-diphenylacrylate, 2-ethylhexyl β,β-diphenylacrylate and ethyl β,β-bis(4-methoxyphenyl)acrylate, the mole ratio of the acrylate to the dibenzoylmethane derivative being not less than 0.8.
 20. In an improved photostable cosmetic screening composition for protection of the human epidermis against ultraviolet rays of wavelengths between 280 and 380 nm, which comprises, in a cosmetically acceptable vehicle containing at least one fatty phase, a dibenzoylmethane derivative, wherein the improvement consists essentially of adding at least 1% by weight of an alkyl β,β-diphenylacrylate or a α-cyano-β,β-diphenylacrylate of formula: ##STR5## in which R₁ and R'₁ which may be identical or different, represent a hydrogen atom, a straight- or branched-chain C₁ -C₈ alkoxy radical or a straight- or branched-chain C₁ -C₄ alkyl radical, R₁ and R'₁ being in the para or meta position;R₂ represents a straight- or branched-chain C₁ -C₁₂ alkyl radical; and R₃ represents hydrogen atom or a --CN radical, to said cosmetically acceptable vehicle consisting essentially of 1 to 5% by weight of dibenzoylmethane derivative, the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative being not less than 0.8, whereby the dibenzoylmethane derivative is stabilized against ultraviolet rays.
 21. A photostable cosmetic screening composition for protection of the human epidermis against ultraviolet rays of wavelengths between 280 and 380 nm, which comprises, in a cosmetically acceptable vehicle containing at least one fatty phase, 1 to 5% by weight of a dibenzoylmethane derivative, said dibenzoylmethane derivative being 4-tert-butyl-4'-methoxydibenzoylmethane, and at least 1% by weight of a α-cyano-β,β-diphenylacrylate of formula: ##STR6## in which R₁ and R'₁ represent a hydrogen atom;R₂ represents a 2-ethylhexyl radical; and R₃ represents a --CN radical, the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative being not less than 0.8.
 22. Cosmetic screening composition according to claim 21, wherein the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative is not more than
 8. 23. Cosmetic screening composition according to claim 21, wherein the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative is between 1.2 and
 8. 24. Cosmetic screening composition according to claim 21, which is in the form of an oily or oleoalcoholic lotion or the form of a fatty or oleoalcoholic gel, of a solid stick, of an emulsion or of a vesicular dispersion of ionic or non-ionic amphiphilic lipids, or is packaged as an aerosol.
 25. Cosmetic screening composition according to claim 21, which contains, in addition, cosmetic adjuvants selected from the group consisting of thickeners, emollients, humectants, sufactants, preservatives, antifoams, fragrances, oils, waxes, lower polyols and monohydric alcohols, propellants, colorings and pigments.
 26. Cosmetic screening composition according to claim 21, which constitutes an emulsion in the form of a cream or milk comprising, as a cosmetic vehicle, fatty alcohols, fatty acid esters, and in particular fatty acid triglycerides, fatty acids, lanolin, natural or synthetic oils and waxes and emulsifiers, in the presence of water.
 27. Cosmetic screening composition in the form of an emulsion or of a vesicular dispersion according to claim 21, which contains, in addition, water-soluble UV screening agents.
 28. Cosmetic screening composition according to claim 21, which constitutes an oily lotion comprising, as a cosmetic vehicle, fatty acid esters, oils and natural or synthetic waxes.
 29. Cosmetic screening composition according to claim 21, which constitutes an oleoalcoholic lotion comprising, as a cosmetic vehicle, oils, waxes or fatty acid esters, and in particular fatty acid triglycerides, and lower polyols, alcohols and/or glycols.
 30. Cosmetic screening composition according to claim 21, which constitutes an oleoalcoholic gel comprising, as a cosmetic vehicle, a natural or synthetic oil or wax, a lower polyol or alcohol and a thickener.
 31. Process for protecting the human epidermis against UV radiation of wavelengths between 280 and 380 nm, which consists in applying to the skin an effective quantity of a cosmetic screening composition as defined in claim
 21. 32. A photostable cosmetic screening composition for protection of the human epidermis against ultraviolet rays of wavelengths between 280 and 380 nm, which consists essentially of a cosmetically acceptable vehicle containing at least one fatty phase, 1 to 5% by weight of a dibenzoylmethane derivative, said dibenzoylmethane derivative being 4-tert-butyl-4'-methoxydibenzoylmethane, and at least 1% by weight of a α-cyano-β,β-diphenylacrylate of formula: ##STR7## in which R₁ and R'₁ represents a hydrogen atom;R₂ represents a 2-ethylhexyl radical; and R₃ represents a --CN radical, the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative being not less than 0.8.
 33. In a photostable cosmetic screening composition for protection of the human epidermis against ultraviolet rays of wavelengths between 280 and 380 nm which consists essentially of a dibenzoylmethane derivative as a UV-A screen in combination with a UV-B screen in a cosmetically acceptable vehicle containing at least one fatty phase, wherein the improvement comprises increasing the protection of the skin against UV rays of wavelengths between 280 and 380 nm by using 1 to 5% by weight of a dibenzoylmethane derivative, said dibenzoylmethane derivative being 4-tert-butyl-4'-methoxydibenzoylmethane, and an effective amount of at least 1% by weight of a α-cyano-β,β-diphenyl-acrylate of formula: ##STR8## in which R₁ and R'₁ represent a hydrogen atom;R₂ represents a 2-ethylhexyl radical; and R₃ represents a --CN radical, the mole ratio of the compound of formula (I) to the dibenzoylmethane derivative being not less than 0.8. 